In recent years, semiconductor devices have become more integrated, and structures of semiconductor elements have become more complicated. Further, a number of layers in multilayer interconnections used for a logical system has been increased. Accordingly, irregularities on a surface of a semiconductor device become increased, so that step heights on the surface of the semiconductor device tend to be larger. This is because, in a manufacturing process of a semiconductor device, a thin film is formed on a semiconductor device, then micromachining processes, such as patterning or forming holes, are performed on the semiconductor device, and these processes are repeated many times to form subsequent thin films on the semiconductor device.
When a number of irregularities is increased on a surface of a semiconductor device, the following problems arise. A thickness of a film formed in a portion having a step is relatively small when a thin film is formed on a semiconductor device. An open circuit is caused by disconnection of interconnections, or a short circuit is caused by insufficient insulation between interconnection layers. As a result, good products cannot be obtained, and yield tends to be reduced. Further, even if a semiconductor device initially works normally, reliability of the semiconductor device is lowered after long-term use. At a time of exposure during a lithography process, if an irradiation surface has irregularities, then a lens unit in an exposure system is locally unfocused. Therefore, if the irregularities of the surface of the semiconductor device are increased, then this becomes problematic in that it is difficult to form a fine pattern itself on the semiconductor device.
Accordingly, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. The most important one of planarizing technologies is CMP (Chemical Mechanical Polishing). In such chemical mechanical polishing, with use of a polishing apparatus, while a polishing liquid containing abrasive particles such as silica (SiO2) therein is supplied onto a polishing surface such as a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing surface, so that the substrate is polished.
This type of polishing apparatus comprises a polishing table having a polishing surface constituted by a polishing pad, and a substrate holding apparatus, which is called as a top ring or a carrier head, for holding a semiconductor wafer. When a semiconductor wafer is polished with such a polishing apparatus, the semiconductor wafer is held and pressed against the polishing table under a predetermined pressure by the substrate holding apparatus. At this time, the polishing table and the substrate holding apparatus are moved relatively to each other to bring the semiconductor wafer into sliding contact with the polishing surface, so that a surface of the semiconductor wafer is polished to a flat mirror finish.
In such a polishing apparatus, if a relative pressing force between the semiconductor wafer being polished and the polishing surface of the polishing pad is not uniform over an entire surface of the semiconductor wafer, then the semiconductor wafer may insufficiently be polished or may excessively be polished at some portions depending on a pressing force applied to those portions of the semiconductor wafer. Therefore, it has been attempted to form a surface, for holding a semiconductor wafer, of a substrate holding apparatus by an elastic membrane made of an elastic material such as rubber and to supply fluid pressure such as air pressure to a backside surface of the elastic membrane to uniformize pressing forces applied to the semiconductor wafer over an entire surface of the semiconductor wafer.
Further, the polishing pad is so elastic that pressing forces applied to a peripheral portion of the semiconductor wafer being polished become non-uniform, and hence only the peripheral portion of the semiconductor wafer may excessively be polished, which is referred to as “edge rounding”. In order to prevent such edge rounding, there has been used a substrate holding apparatus in which a semiconductor wafer is held at its peripheral portion by a guide ring or a retainer ring, and an annular portion of the polishing surface that corresponds to the peripheral portion of the semiconductor wafer is pressed by the guide ring or retainer ring.
A thickness of a thin film formed on a surface of a semiconductor wafer varies from position to position in a radial direction of the semiconductor wafer depending on a film deposition method or characteristics of a film deposition apparatus. Specifically, the thin film has a film thickness distribution in the radial direction of the semiconductor wafer. Since a conventional substrate holding apparatus, as described above, for uniformly pressing an entire surface of a semiconductor wafer polishes the semiconductor wafer uniformly over the entire surface thereof, it cannot realize a polishing amount distribution that is equal to the aforementioned film thickness distribution on the surface of the semiconductor wafer. Therefore, the conventional polishing apparatus cannot sufficiently cope with the film thickness distribution in the radial direction, and insufficient or excessive polishing is caused.
Further, the aforementioned film thickness distribution on the surface of the semiconductor wafer varies depending on a type of a film deposition method or a film deposition apparatus. Specifically, positions and a number of portions having a large film thickness in a radial direction and differences in thickness between thin film portions and thick film portions vary depending on the type of a film deposition method or the film deposition apparatus. Therefore, a substrate holding apparatus capable of easily coping with various film thickness distributions at low cost has been required rather than a substrate holding apparatus capable of coping with only a specific film thickness distribution.
In a substrate holding apparatus having a structure for pressing a portion of a polishing surface that corresponds to a peripheral portion of a semiconductor wafer by a guide ring or retainer ring in order to prevent edge rounding, non-uniform polishing such as edge rounding cannot sufficiently be suppressed in some cases by merely controlling pressing forces of the aforementioned guide ring or retainer ring. Generally, no devices are formed on a peripheral portion of a semiconductor wafer. Nevertheless, for a purpose of preventing elution of metal or other defects, it is required that a polishing rate is intentionally reduced at a peripheral portion of a semiconductor wafer so that an underlayer film is not exposed, or, on the contrary, a polishing rate is intentionally increased at a peripheral potion of a semiconductor wafer so as to remove a film on the peripheral potion of the semiconductor wafer. A conventional polishing apparatus cannot sufficiently control a polishing rate at a peripheral potion of a semiconductor wafer to a desired level.